Two-minute dip leaves traders searching for trigger

A sudden plunge by Chinese mainland stocks in Hong Kong had traders scrambling to find a trigger for the slump that coincided with a surge in futures volumes.

The Hang Seng China Enterprises Index tracking some of the nation's biggest companies tumbled from an advance of 1 percent to a loss of 1.5 percent in about two minutes, shortly after 2 pm, before rebounding to a gain.

Stocks including Tsingtao Brewery Co and PetroChina Co fell sharply in Hong Kong before paring losses. The same shares in Shanghai didn't replicate the move.